The present invention relates to an overhead powerline survey method and, in particular, to a survey method for the design and maintenance of overhead powerlines, including survey of a line from points off the line so that the route of the line and the local topography in the vicinity of the line may be recorded.
Traditionally, surveying of existing powerlines or of the route of planned powerlines is restricted to following only the exact route of the powerline by sighting from one point on the line to the next, along the route of the line. The traditional methodology allows only very limited account to be taken of local topographical features, e.g., roads, houses and the like. Measurements taken in powerline surveys are generally recorded manually in a logbook and computed at a later time to derive two-dimensional co-ordinates for the points measured, i.e., height and distance along the line. These co-ordinates are then plotted using traditional drafting techniques. If it is required to input this data into a computerized system, the transfer has to be done manually.
The positions of the required support structures for a proposed powerline may then be defined on this plot. Then the line of the conductor is plotted and ground clearance is checked. If sufficient clearance has been obtained, this design is accepted and the relevant materials ordered so as to construct the powerline.
This paper based system has a number of inherent shortcomings. These are:
The whole design process takes place in two dimensions whereas in reality three dimensional data should be used.
Modifying a proposed design is time consuming and costly.
The whole process is slow.
The transcription of data and manual computation of coordinates and drafting thereof is prone to error.
The survey technique requires that a corridor along the proposed route be cleared completely of vegetation, so as to establish a clear line of sight.
The survey technique does not take full account of features offset from the route of the line.
The design process takes place in a scaled plot, not at actual scale, thereby introducing errors due to the poor definition of the features plotted.
The conductors are modelled using fixed parameters.
These cannot be easily altered to take account of varying limits.
The cost of the proposed line is not calculated until the design has been accepted.